California’s Snowpack Is a ‘Water Supply Dream’

California has a history of years-long dry spells and wet winters, a pattern illustrated at Phillips Ranch over the decades

By Jonathan Lloyd •Published April 3, 2019•Updated on April 3, 2019 at 8:45 am

California Department of Water Resources

The numbers from the most recent survey of snow levels in the Sierra Nevada Mountains in California are staggering, but not unexpected after a winter of unrelenting storms.

Tuesday's manual survey at Phillips Ranch showed snowpack at 200 percent of average for that location. Statewide, snowpack was at 162 precent of average. The state's six largest water reservoirs hold between 106 and 132 percent of historical averages for early April.

"With full reservoirs and a dense snowpack, this year is practically a California water supply dream," said Department of Water Resources Director Karla Nemeth. "However, we know our long-term water supply reliability cannot rely on annual snowpack alone. It will take an all-of-the-above approach to build resiliency for the future."

California has a history of dry spells and wet rain seasons, a pattern on display at Phillips Ranch over the decades. Some surveys were conducted in fields of brown grass. Others required the survey team to trudge through deep snow drifts to reach the survey site.

The manual surveys, just off Highway 50 near Sierra-at-Tahoe, are done each winter near the start of January, February, March and April. Manual and electronic readings are taken at other sites in the mountains.

The snow along the 400-mile Sierra mountain range melts in the spring in a traditional wet season, runs off into reservoirs ahead of the state's dry, hot summers and provides about 30 percent of California's water. Water managers use a measurement called "snow water equivalent," which is the depth of water that theoretically would result if the entire snowpack melted at once.

The Phillips Ranch survey showed a snow water equivalent of 51 inches, which is 200 percent of average. That's nearly triple the snow water equivalent from Feb. 1.

The April 3 survey recorded 106.5 inches of snow depth.

The monster snowpack brings concerns about flooding this spring.

"With great water supply benefits comes some risk,” said Jon Ericson, DWR Chief of the Division of Flood Management. "Based on snowpack numbers, we have the potential for some minor flooding due to melting snow so we remind folks to always stay vigilant and aware."

A weather phenomenon called an atmospheric river is a major reason for the puffed up pillow of snow in California's mountains. The bands of moisture in the sky over the Pacific that fuel colossal rain-making storms have contributed to some of California's wettest winters. Storms draw moisture from the rivers as they move toward California, sometimes unleashing days of steady rain on the West Coast.

California has had more than 30 atmospheric rivers since the start of the water year in the fall with six in February alone, according to the department of water resources.

In mid-March, California was free of drought for the first time since Dec. 20, 2011, according to the National Drought Mitigation Center. Just three months ago, 75 percent of the state was in moderate to extreme drought.

Researchers for California’s Fourth Climate Change Assessment last year noted that the state has a “highly variable climate” with wet or dry periods that can span years and that are “heavily affected by extreme precipitation events.”

“As the climate continues to warm, atmospheric rivers, responsible for many of the heaviest extremes, will carry more moisture and extreme precipitation may increase,” the assessment says.

But warming air can also exacerbate periods of drought.

One group of researchers last year dubbed the change from extreme dry to wet conditions in the state as “precipitation whiplash events,” Quartz reported.

In 2014, then-Gov. Jerry Brown declared a drought emergency for California, ordering prohibitions on wasteful water use like hosing off driveways and sidewalks, and watering lawns within days of a rainstorm, after a several dry years. That emergency order was lifted for most of the state in 2017 after a historically wet winter.